BF 3 is alive
In the trailer embedded above, you can see what will be possible in Battlefield 3 with the framework called “Venice Unleashed” (VU). Not only can you use it to create your own maps and vehicles, but also modify existing ones or even create completely new game modes.
The video shows, among other things, a replica of the Counter-Strike map de_dust2, as well as a bicycle and a modified buggy. But that doesn't stop there: The entire gameplay can also be rebuilt. This is shown, for example, by a top-down shooter in which you shoot waves of AI-controlled opponents.